Electric wave signaling system



March 1, 1932.

W. A. MARRISON ELECTRIC WAVE SIGNALING SYSTEM Filed Sept. 2, 1924 //7l ?/7/0/.' Warm/7 A Mar/1300 Patented Mar. 1, 1932 UNITED STATES PATENT OFFICE WARREN A. MARRISON, OF EAST ORANGE, NEW JERSEY, ASSIGNOR T0 WESTERN ELEG- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CGRPORATION OF NEW 'YORK ELECTRIC WAVE SIGNALING SYSTEM Application filed September 2, 1924. Serial No. 735,268.

This invention relates to electric wave signaling systems, and more particularly, to signal receiving systems including improved frequency control means.

By virtue of the low temperature co-efiicient of elasticity and of expansion of certain piezo-electric substances and because of the exceedingly low elastic hysteresis of piezo crystal substances, they offer many advantages for use in circuits requiring high frequency stability and sharp frequency characteristics. The utility of these substances is still further enhanced by their peculiar properties, whereby they may be set into me chanical vibration at their natural frequencies by the action of varying electric forces. Piezo electric devices employing quartz crystals may be utilized to great advantage in certain signaling systems, as for example, carrier wave receiving systems, either wire or radio, operating with carrier waves of high or low frequencies. vVhen quartz piezo crystals are used in the detecting element of receiving systems, numerous advantages are secured, particularly in systems arranged for single side band transmission. In such systems the factor of frequency stability is particularly important because the locally supplied oscillations must be maintained at the frequency of the original carrier or at a con stant frequency difference therefrom.

An object of the present invention is to maintain substantially constant the frequency of waves supplied locally to a carrier wave receiving system.

Another object is to supply carrier waves to a detecting device that are unvarying as regards frequency.

A further object is to control the frequency of waves generated in a detecting system by means of piezo electric devices.

A feature of the invention relates to a space discharge tube system arranged to function both as a detector and as an oscillator under control, as to frequency, of a quartz piezo-electric device.

The invention is applicable to wire or radio systems and in its preferred form employs space discharge devices for performing such functions as energy detection, os-

cillation generation and wave amplification. The function of frequency control over waves generated in the system is performed by piezo-electric devices preferably utilizmg quartz crystals as their vibratory elements. More specifically, a wave receiving conductor such as a wire line or antenna is coupled to the input circuit of a space dis charge tube arranged to be self-oscillating. In the input circuit, waves collected by the receiving conductor are combined with waves generated in the oscillatory system. A piezoelectric crystal, preferably of quartz, is arranged so as to be capable of mechanical vibration in the field between metallic plates connected to electrodes of the space discharge tube. The natural frequency of the vibration of the crystal then determines the frequency of oscillations generated. This frequency remains constant within narrow limits because of the properties of the crystal already described. The space discharge tube acts to detect the low frequency modulations of received waves which may be transmitted to a wire line or to a signal receiver.

A detailed description of the invention follows in which reference is made to the drawings wherein:

Fig. 1 represents a radio receiving system provided with a piezoelectric frequency control element;

Fig. 2 is a circuit diagram of a system similar to Fig. 1 wherein the first tube functions as an amplifier and oscillator;

Fig. 3 is a circuit diagram of asystem similar to Fig. 2 providing tuned radio frequency coupling between the tubes;

Fig. 4 is a circuit diagram of a radio receiving system having a separate tube for generating local oscillations;

Fig. 5 is a circuit diagram of a system similar to Fig. 4 wherein the detector is trans former coupled to the amplifier and oscillator.

Like reference characters have been used in the various figures of the drawings to indicate like parts.

The system illustrated in Fig. 1 comprises a wave receiving conductor 10 coupled to the space discharge tube dectector 15 arranged to supply signaling waves to a space dis charge tube amplifier 20 having included in its output circuit a signal receiver 25. The wave receiving conductor 10, which is illustrated as an antenna, may also be a wire line or similar device. The antenna 10 is connected to ground in series with the primary winding of transformer 11. The secondary winding of transformer 11 has its mid-point connected to the filament of tube in series with a grid polarizing battery 12. The outer terminals of the secondary winding are connected to the terminals of adjustable condenser 13 which are in turn connected respectively to the anode and grid of tube 15. The lead connecting to the anode includes piezo electric device 14 having a quartz crys tal 16 positioned between metallic plates 17 and 18 in such manner as to be capable of mechanical vibration. The piezo-electric device 14: is arranged to compensate the grid plate capacity of tube 15 at frequencies other than the natural frequency desired. The tuned circuit formed by transformer 11 and condenser 18 cooperates with the device it to select the one of its natural frequencies at which oscillations shall be generated.

The shape and dimensions of the crystal are so designed that it has a natural frequency of vibration corresponding to the frequency of desired oscillations. The manner of connecting the piezo-electric device 1 1 and an explanation of its operation in controlling the frequency of oscillations is given in my copending application, Serial No. 730,165, filed August 5, 1924. An output circuit is connected to the anode and cathode of tube 15 which includes a space current source 19 here illustrated as a battery in series with the primary winding of a low frequency transformer 21. A low frequency amplifier comprises thespace discharge tube 20 having an inputcircuit connected to its cathode and grid which includes the secondary winding of the transformer 21 in series with grid polarizing'battery 22. Space current is supplied to tube 20 by a battery 23 in series with low frequency cholre coil 24 connected to the anode and cathode of the tube. A signal receiving device 25 in series with a blocking condenser 26 is also connected to the anode and cathode of tube 20. Condenser 26 serves to prevent direct current produced by battery 23 from flowing in through receiver 25.

Condenser 27 is arranged to be connected in shunt to the second ry winding of transformer 21 by closure of switch 28. This condenser functions to provide a resonant circuit with the secondary winding of the transformer which may be tuned to the mean of the low frequencies produced in the output circuit of detector 15. This condenser may also function to suppress undesired oscillations in the circuit of amplifier 20 and also to provide in cooperation with battery 22, a desired potential upon the grid of tube 20.

The antenna 10 is arranged to receive signal modulated waves and to supply the received waves to the input circuit of the de tector 15. The received waves may comprise only a single side band produced by the modulation of a carrier wave by waves of different frequency representing signals or they may comprise both side bands either with or without an unmodulated component of carrier frequency, the advantages of both such modes of transmission being known. Gondenser 13 together with the secondarv winding of transformer 11 form a resonant circuit which is preferably tuned to a frequency corresponding to the mid-frequency of the received single side band.

By virtue of the feed-back coupling between input and output circuits of tube 15 supplied by device 14 oscillations are generated in the system. The frequency of these oscillations is determined by the natural frequency of vibration of piezo-electric device l4 and is preferably the same as the frequency of the original carrier wave from which the received side band is derived. The battery 12 is preferably of such a potential that the tube 15 will operate upon a portion of its characteristic curve whereby, when the locally generated waves are combined with the received side hand, there will be produced in the output circuit of the tube waves corresponding in frequency and amplitude to the original modulating waves. These waves are transmitted through transformer 21 and supplied to the input circuit of tube 20. Battery 22 in this input circuit is adjusted so that tube 20 operates upon the straight portion of its characteristic curve. There then appear in the output circuit of tube 20, Waves corresponding to those supplied to its input circuit, but increased in amplitude. These waves actuate the receiving device 25 to produce audible sounds corresponding to signals transmitted from the distant station.

By virtue of the action of piezo-electric device 14, the frequency of locally generated waves may be maintained substantially constant and therefore in almost exact synchronism with the original carrier waves produced at the transmitting station. It is to be noted that the piezo-electric device let is positioned outside the path traversed by low frequency waves and hence offers no impedance thereto.

The transformer 21 preferably has a low impedance primary and a highimpedance secondary. This transformer is preferably designed to be efiicient at frequencies within the audible range. V

In Fig. 2 the antenna 10 is coupled to a high frequency amplifier oscillator 15'. The circuit associated with the tube 15 is substantially the same as the circuit associated with modulating waves.

the detector 15. However, battery 12 is of such potential as to cause the tube 15 to operate upon the straight portion of its characteristic curve. As a result the received waves together with locally generated waves are transmitted to the output circuit of the tube unaltered in frequency, but increased in amplitude. These waves are supplied through the coupling network constituted by condenser 29 and shunt impedances 30 and 31 to the input circuit of the space discharge tube demodulator 32. Space current is supplied to tube 32 by a battery 33 in series with the choke coil 34. Terminals 35 and 36 which are connected to the anode and cathode of tube 32 are arranged to be connected to a wire line or signal receiving device.

A battery .37 in the input circuit of tube 32 is preferably of such potential that tube 32 operates upon a curved portion of its characteristic. The received waves and locally generated waves transmitted from amplifier 15 are then combined in the tube 32 to produce waves corresponding to the original These waves are then supplied from the output circuit of tube 32 to the wire line or receiving device connected to terminals 35 and 36.

The receiving circuit illustrated in Fig. 3 is identical with that illustrated in Fig. 2 with the exception that the condenser 29 is omitted and the impedances 30 and 31 are replaced by the windings of a high frequency transformer 21 and the secondary winding of this transformer is shunted by a variable condenser 27. By means of this condenser the input circuit of tube 32 may be tuned to the frequency of carrier waves, or the midfrequency of one side band and especially in the case of single side band transmission to the mid-frequency of the side band, thereby increasing its selectivity thereto.

In Fig. 4 the tube 15 is arranged in a circuit which is very similar to the circuit associated with tubes 15 in Figs. 2 and 3, but in this figure the tube serves only to supply local oscillations tobe combined with the received waves. The coil 11 is not couple-d to-the antenna. An additional tube 38 is arranged to amplify the received waves. This tube includes an input circuit connected to its cathode and control electrode including a resonant circuit 39 and a grid polarizing battery 40. The resonant circuit 39 is coupled to the antenna by means of a transformer 41, the secondary winding of which forms the inductive element of the resonant circuit 39. The other element of this resonant circuit is a variable condenser 42. The remainder of this circuit is identical with the corresponding portion of the circuit of Fig. 2.

Received waves are transmitted from the antenna 10 to the amplifier 38 and from the amplifier they are transmitted to the input circuit of tube 32. Locally generated waves produced by oscillator 15' are likewise supplied to this input circuit. By virtue of the demodulating action of tube- 32 waves corresponding to the original modulating waves are produced in its output circuit. These waves are then supplied to a wire line or other device connected to the terminals 35 and 36.

In the circuit shown in Fig. 5 the anodes of tubes 15' and 38 are connected in series to the terminals of the primary winding of transformer 43. The mid-point of this winding is connected to the cathodes of tubes 15' and 38 by a path including space current battery 37. The secondary winding of transformer 43 is included in the input circuit of detector 32 which is connected to its grid and cathode. This secondary winding is arranged in a resonant circuit with adjustable condenser 27'. A suitable average potential is maintained upon the grid of tube 32 by a grid leak 44 in shunt to a blocking condenser 45. In other respects this circuit corresponds to the circuit shown in Fig. 4 and functions in a similar manner.

What is claimed is:

In an electric wave signaling system, a receiving conductor, a space discharge tube, said tube having input and output circuits coupled to said conductor, means for causing said tube to function as a detector of received waves to produce an audible signal and means for causing said tube to function also as a wave generator, said last mentioned means including a piezo-electric device arranged to compensate the capacity bet-ween input and output circuits of said tube at fre uencies other than the natural frequencies 0 vibration of said device.

In witness whereof, I hereunto subscribe my name this 26th day of Au ust A. D., 1924.

WARREN A. ARRISON. 

